runtime: implement v0.6.x ext_ functions

[noot]

Expected Behavior

imports_old.go (previous ext functions)

• ext_is_validator
• ext_local_storage_get
• ext_local_storage_compare_and_set
• ext_network_state
• ext_submit_transaction
• ext_local_storage_set

imports.go (new ext functions that are ready to be implemented)

• ext_kill_child_storage
• ext_child_storage_root
• ext_clear_child_storage
• ext_get_allocated_child_storage
• ext_secp256k1_ecdsa_recover_compressed
• ext_log

New ext functions that are not specced yet (please create a new issue with the following fns in it when the above functions are implemented)

• ext_sandbox_memory_new
• ext_sandbox_memory_teardown
• ext_sandbox_instantiate
• ext_sandbox_invoke
• ext_sandbox_instance_teardown
• ext_sandbox_memory_get
• ext_sandbox_memory_set

It will also be a good idea to look at the v0.7 ext_ functions (see spec Appendix E) to see what changes we will need to make to upgrade, and make the v0.6 functions easily wrappable for v0.7.

Checklist

• I have read CONTRIBUTING and CODE_OF_CONDUCT
• I have provided as much information as possible and necessary
• I am planning to submit a pull request to fix this issue myself

[edwardmack]

Items remaining undone on checklist because these have not been spec'd yet.